Some aircraft, both fixed-wing and rotary aircraft, include one or more propeller blades driven by a gas turbine engine. Such aircraft may include a hydraulically actuated propeller pitch control actuation system that is configured to adjust and maintain a pitch of the propeller blades. Generally, the pitch of the propeller blades corresponds to an amount of thrust generated by the propeller blades. In some aircraft, the blade pitch angle can be reversed. This causes the engine to generate a reverse thrust, which can be used to help slow the aircraft after landing.
As may be appreciated, reverse thrust propeller pitch angle is preferably prevented on fixed wing aircraft, unless or until the aircraft is on the ground. To provide this functionality, the aircraft will include a mechanism, independent of the primary propeller pitch control architecture, to prevent unintended thrust reversal. One particular mechanism that is presently used is a pin that is inserted into a hole or slot to mechanically prevent the propeller pitch control actuator from commanding reverse pitch positions. The position of the pin is controlled by a solenoid that retracts the pin, allowing the actuator to travel to reverse prop pitch positions.
Although the above-described architecture is generally effective, it does exhibit certain drawbacks. For example, it is relatively heavy and relatively costly. Hence, there is a need for a propeller pitch control actuation system that includes a relatively lightweight, relatively inexpensive means for selectively preventing the propeller pitch control actuator from commanding reverse pitch positions. The present invention addresses at least this need.